The communications industry has seen a rapid growth in networked computer systems with an interactive user interface. One example of such an interactive system is the World Wide Web. However, for a variety of reasons, interactive systems may suffer from response delays which are delays from the time information is requested until the information is displayed to a user. Response delays are typically associated with a user making a request for information and then experiencing a delay while waiting for the information to be retrieved from a remote source, decoded and presented. An example of a system in which response delays are fairly common is the World Wide Web (WWW), as discussed below.
The WWW, which is one of several service facilities provided on top of the Internet, is a hypermedia facility that allows users to browse web pages through a graphical user interface (GUI) called a web browser. The WWW is a client-server based network that comprises a number of servers 12 (e.g., computers connected to the Internet) on which web pages or files reside and a number of clients 14 (e.g. web browsers) which interface the users with the web pages. A web browser is a software application such as WebExplorer.RTM. (IBM Corporation) or Netscape Navigator.RTM. (Netscape Communication Corporation) that operates on a client 14 and that typically sends a request over the Internet to a server 12 requesting a copy of a web page identified by a uniform resource locator (URL). The URL describes both the server 12 where the web page resides and the information that is being requested. In response, the server 12 sends a copy of the requested information to the web browser which displays the web page to the user.
Web pages on the WWW may be hyper-media documents written in a standardized language called hypertext markup language (HTML). A typical web page includes text together with embedded formatting commands, referred to as tags, which can be used to control the font size, the font style (for example, whether italic or bold), the layout of the text or other document attributes. A web browser parses the HTML in order to display the text in accordance with the specified format. In addition, a web page can also contain a reference, in terms of another URL, to a piece of multimedia data, for example, an image, a video segment, or an audio file. The web browser responds to such a reference by retrieving and displaying or playing the data. This often requires the web browser to launch another software application such as a plug-in or helper program that is particularly configured for displaying or playing the multimedia data as formatted. For example, RealAudio.TM. Player (Progressive Networks) is a plug-in application that allows a user to download and play streaming audio in real-time over the WWW using streaming media technology. Alternatively, such multimedia data may form its own web page, without any surrounding HTML text.
Some web pages also contain one or more references to other web pages which need not be on the same server as the original web page. Such references may generally be activated by the user selecting a particular location on the screen, typically by clicking a primary button of a pointing device such as a mouse. These references or locations are known as hyperlinks, and are typically flagged by the browser in a particular manner (for example, any text associated with a hyperlink may be in a different color or underlined). If the user selects the hyperlink, then the referenced page is retrieved and replaces the currently displayed page. Further information about HTML and the WWW can be found in World Wide Web and HTML by Douglas MacArthur, pp. 18-26 and Dr. Dobbs' Journal, December 1994, and in The HTML Sourcebook by Ian Graham, John Wiley Publishers, New York, USA (1995).
In an effort to increase the interactive nature and to enhance the experience of the WWW, recent developments in hyper-media technology have brought about innovations such as Java.TM. (Sun Microsystems, Inc.) and virtual reality modeling language (VRML, pronounced "ver-mel"). Java technology, for instance, comprises primarily (i) a new programming language, somewhat similar to C and C++, and (ii) a virtual machine. Essentially, programs written in the Java programming language can be compiled into byte code form, and then interpreted at runtime on a Java virtual machine. The Java virtual machine converts the byte codes into instructions that can be executed by the underlying physical machine.
Programs written using Java can be downloaded over the WWW in the form of byte codes for execution on a Java virtual machine at the client 14. Such programs are known as "applets". The use of the Java technology for downloading code over the WWW has two major benefits. Firstly, an applet can be platform independent, if we assume that each client 14 has a copy of the Java virtual machine (the virtual machine at the client's system is typically incorporated either into the operating system, or into the web browser itself). In other words, there is no need for a server 12 to have different versions of the code for downloading to clients 14 according to their respective operating systems and machines. Therefore, only a single version of the relevant code needs to be written and maintained at the server 12, which makes life much simpler for software developers. Secondly, because the applet executes on a virtual machine, rather than a physical machine, security is greatly improved. Thus, when downloading code over the network, there is always a risk that it will include some malicious code (accidentally or otherwise) that may damage data or programs stored at the client. The virtual machine, however, can monitor the operation of the applet to detect and prevent such malicious activity.
It will be noted that the concept of downloading software from a server to a client in the form of byte codes for execution on a virtual machine was also known independently of the Java technology as described, for example, in U.S. Pat. No. 5,347,632.
In order to invoke a Java applet, a web page of HTML text contains an &lt;APPLET&gt; tag, which identifies the URL containing the applet. A browser responds to this tag by retrieving and running the applet. Also defined is a &lt;PARAM&gt; tag, which is contained within a pair of corresponding &lt;APPLET&gt; and &lt;/APPLET&gt; tags, and which can be used to specify parameters that are passed to the applet at run-time. (Note that the APPLET and PARAM tags are not formally incorporated into the HTML standard, but are nevertheless recognised by many web browsers). Further information about the Java technology and applets can be found in "Teach Yourself Java in 21 Days" by Laura Lemay and Charles Perkins, Sams.Net Publishing, Indianapolis, USA (1996).
Out of an effort to heighten the sensory experience of the WWW, three dimensional virtual reality languages have also begun to be developed. One such language is VRML. VRML is a standardized language for describing the animation and three dimensional modeling of geometric objects. VRML allows a three dimensional scene(s) or world(s) to be manipulated in an interactive manner over the Internet and shared by multiple users. Thus, unlike HTML which provides for merely formatting text and images, and for hyperlinks to other web pages, VRML provides for the organization and interaction of three dimensional objects and scenes in a hierarchical fashion within a virtual three dimensional space.
A VRML browser is used to view a three dimensional virtual world constructed using VRML. The VRML browser may be a helper program or plug-in to a web browser that is launched when the web browser detects that a file being downloaded is a VRML document. The VRML browser provides means for allowing the user to move around or navigate the three dimensional virtual world. Typical navigation controls for a VRML browser include walk, spin, look, slide, and point. Typically, the walk control allows the user to move forward and backward within a world, the spin control allows the user to turn in an arcuate fashion within a world, the look control allows the user to zoom in or pan out from a particular area within a world, the slide control allows the user to move sideways in an arcuate fashion within a world, and the point control allows the user to return to his/her initial vantage point within a world.
One problem brought about by the development of WWW technologies such as Java and VRML is that they may require the transfer of relatively large amounts of data from the server 12 to the client 14. When coupled with increased traffic caused by the rapid growth in the number of users on the Internet, the results are lengthier delays which are both variable and unpredictable. During the delay, the user is typically left with some sort of a busy indicator, such as an hour glass pointing device. During the delay, the user is often times not able to perform any other operations. This often leads to user frustration and annoyance. It has been recognized that a key to user satisfaction in an interactive system is maintaining a consistent response time. See, for example, "User Behavior On An Interactive Computer System", S. J. Boies, IBM Systems Journal, Vol. 13, No. 1, pp. 2-18 (1974).
This problem is the result of many factors including the current physical and practical limits in transmission speeds (i.e., bandwidth) available on the WWW. Particularly, the connection between a client and his/her access provider or gateway to the Internet is usually not shared, or only lightly shared, by other users and can transmit data relatively fast even though the transmission rate may be relatively slow (e.g., 56 kilobits per second or slower). However, the connection between the access provider, or gateway, and the server where the requested data resides is usually a high traffic link that is shared by many users and that may carry an unpredictable volume of traffic. Moreover, the server where the requested data resides may itself have a variable response time that further delays the retrieval of the data. Therefore, the interactive experience provided by the WWW may be overshadowed by the delays that the user may have to endure when downloading a web page or perform other tasks on the Internet.
In other systems, such as interactive television or proprietary online services (e.g., those services provided by America OnLine, Inc. or Compuserve, Inc.), similar problems may exist where the end user experiences delays while requester input data is processed. For example, in an interactive television system, an end-user may request a customized listing of movies from a database that meets a user-defined set of parameters. Depending upon a variety of factors such as the communication medium utilized, the size and complexity of the database search, and the traffic characteristics of the system, the user may experience a delay from several seconds to more than a minute while waiting for the list to be provided.
In view of the above discussion, improvements are needed in addressing the delays that users experience when using interactive systems.